There are many uses for feeders which automatically infuse solid solutes into liquid solvents, as for instance in the addition of chlorine bearing compounds and other chemical additives to swimming pools, the addition of anti-pollution agents to potable or other surface water supplies, the infusion of solid, soluble chemicals into various circulating liquids to enrich the same in industrial chemical processes and in the addition of consumable anti-corrosion additives in air conditioning systems.
In each such instance, the rate of addition of the solute and its concentration must be carefully controlled within relatively narrow limits. However, under many conditions, the range of feed rates and concentrations must be adjustably controlled within extremely wide ranges, although the particular feed rate and concentration at any one time must be maintained within narrow limits. For instance, in swimming pools, the concentration of chlorine must be controlled within relatively narrow predetermined limits. However, the rate of infusion of chlorine bearing compounds is dependent upon many factors including but not limited to ambient temperature and the extent of use of the pool which tends to destroy or consume chlorine. Moreover, under given conditions, some swimming pools require a "shock" treatment of chlorine or other additives, wherein the rate of addition and the concentration of the additive far exceeds the rate and concentration maintained under normal operating conditions. Thus, a feeder supplying a solid, soluble chlorine compound and other additives to a swimming pool must be sufficiently adjustable to accommodate for widely varying demands in the range of both the rate of supply and concentration of chlorine yet maintained at any one time, the rate of supply and concentration within relatively narrow limits.
Another vital consideration for such feeders is the frequency with which the feeder must be attended to replenish the supply of solute or to alter the program for both the rate of addition of solute and the identity of the solute added. Obviously, it is desirable to increase the time between attendance for either replenishing the supply of solute or altering the program of addition consistent with the size of the feeder and the cost of the same. Thus, it is an object of the present invention to provide means to store sufficient solute for relatively long term operation and to infuse small quantities thereof under precisely controlled conditions. In addition, the said means are adapted to automatically alter the program of addition, varying not only the rate of delivery and hence, concentration, but also the identity of the solute added over relatively long periods of time without manual attendance.
The feeder described and claimed herein employs tablets of solid solute which have a predetermined, relatively precisely controlled rate of dissolution in the solvent under given conditions of concentration and temperature. The rate of dissolution of such tablets may be altered by well known techniques in the manufacture of the tablets.
The feeder includes a housing containing a predetermined, controlled quantity of solvent with means for circulating solvent through the housing at a controlled predetermined rate. A tablet feeding canister containing a relatively long-term supply of tablets is mounted in the housing with one or more tablets exposed to the solvent in the housing. The level of solvent is maintained within narrow limits by means of a float valve. The concentration of solute in the solvent is a function of its solubility in the solvent. The rate of supply of solute to the solvent in the reservoir supplying the feeder is a function of the rate of dissolution of the solute tablet which in turn is a function of, the surface area of solute tablet exposed to the solvent in the feeder the solubility of the tablet itself, the concentration of the solute in the solvent and, to a limited degree, the rate of circulation of solvent through the feeder as it affects the concentration of solute in the solvent. The parameter most easily controlled is the surface area of the solute tablet exposed to the solvent in the feeder which, in the invention described and claimed herein, is a function of the solvent level in the housing of the feeder. In addition, the rate of supply of solute may also be controlled to a large extent by the basic rate of dissolution of the solute tablet as determined by its constituents and manner of manufacture.
The quantity of level of solvent in the feeder, the surface area of solute exposed to the solvent, the rate of circulation of solvent through the feeder and the rate of dissolution of the tablet can be balanced such that the concentration of the solute in the solvent reservoir may be maintained within narrow limits. However, means are also provided for either manually or automatically changing various parameters to change the rate of delivery of the solute to the solvent reservoir. Moreover, means are provided to prevent the undesired syphoning of all of the solvent from the feeder housing, which can create difficulties of priming the pump supplying solvent to the feeder. Nevertheless, if circulation of solvent in the feeder is terminated, means are provided for breaking contact between the solid solute and the solvent. This is particularly important under conditions, such as those commonly found in swimming pool applications, where the interaction of the solute with the solvent under stagnant conditions over a long period of time can result in the formation of an undesirable and potentially dangerous gas.